Sensors have been around for many years for detecting a change of state. Security sensors, which detect a change of state when a door or window has been opened during an unauthorized time, or in some other unauthorized conditions, have routinely been used as part of a security system. Traditionally, intrusion of a door or window has been sensed by a break in an electromagnetic circuit using a device, such as a reed switch installed in one portion of the window or door (the frame or closure between the frame) and a magnet installed in the other portion of the window or door.
Sensors can be either hard wired or wireless as part of the security system. Known wireless sensors, even those intended to be hidden to some degree, are quite large. For example, known wireless security sensors, such as the ITI Recessed Micro Door Window Sensor (model 60-741-95) [Interactive Technologies, Inc. of North Saint Paul, Minn.] or Ademco Recessed Transmitter (model no. 5818) [Alarm Device Manufacturing Company of Syosset, N.Y.] have overall lengths of 3.8 inches and 4⅞ inches, respectively.
The Applicant's co-pending U.S. patent application Ser. No. 09/994,048 (“'048”), filed Nov. 27, 2001, and entitled “Wireless Security Sensor System,” discloses a concealed, wireless security sensor positioned within windows and doors. The '048 patent application discloses a wireless security sensor system that has a wireless security sensor (in preferred form, a reed switch and magnet assembly) inserted into a hollow interior forming part of a window or door frame and that the exposed face of the sensor or the magnet assembly is nearly flush with the inner core of the frame that defines the hollow opening. The other complementary component (the reed switch or magnet assembly) is inserted within a closure device (the window or the door) to which the closure device moves relative to the frame between the open and closed positions.
The complementary component also has a face that is nearly flush with the perimeter surface of the closure such that the two faces of the complementary components are facing each other when the closure is in the closed position relative to the frame. When the face of the component containing the sensor is in the closed position and aligned with the face of the component containing the magnet assembly, the reed switch of the sensor closes in the presence of the magnetic field between the sensor and the magnetic assembly. A microprocessor monitors the state of the reed switch. When the closure is in the open position, the magnetic field is removed, and the reed switch opens, which in turn sends a signal to a wireless transmitter. The wireless transmitter may, in turn, transmit a signal to a receiving panel capable of emitting an audible alarm signal and/or a signal to security or police to indicate that the window/door has been opened.
The '048 patent application discloses that good placement of a wireless security sensor is within the inner and outer walls (or skins) of the window frame with a front face of the sensor housing positioned nearly flush with the inner wall of the window (or door) frame. In doing so, the sensor is hidden within the frame and is not readily seen to an intruder. Additionally, a wire antenna can be positioned within the hollow portion between the window or door frame so as to take up less space and be less conspicuous.
The afore-mentioned '048 patent application security system is useful for installation at the time of manufacturing where the size of the window may be made to accommodate the size of the wireless sensor. However, standard manufactured windows have a frame width between the interior and exterior wall or skins that are approximately ½ to 1 inch thick. Conventional wireless sensors, with lengths of 4–5 inches, can pierce the exterior skin of the frame when the face of the sensor is positioned nearly flush with the interior skin. And piercing the outer skin after the window/door leaves the manufacturer's shop may void window/door manufacturers' warranties by breaking the water seal provided by the manufacturers. Voiding a manufacturer's warranty is highly undesirable for security device manufacturers and installers. Such risk reduces the likelihood of obtaining after-market, concealed, wireless security systems.
Furthermore, size of the conventional wireless sensors is highly contingent on the sensor's power source. In the afore-mentioned ITI and Ademco wireless sensors, long life, high capacity, lithium batteries, namely, 3V lithium 123A batteries, such as Panasonic CR 123A or Duracell DL 123A models, are used as the power source. These lithium batteries have sufficient capacity to provide a long life, e.g., greater than 5 years, but are relatively large. These type batteries typically measure 60 mm long, (slightly under 2½ inches). In conjunction with the battery, the sensor switch and electronic components all add up to a sensor length of approximately 4 to 5 inches. If a smaller sized battery is used to create a smaller sensor, compensatory measures will need to be added if battery life span is not to be sacrificed.